1. Field of the Invention
The present invention relates to a method of compensating the interval between pixels of an image recording apparatus, and, more particularly, to a method of compensating the interval of pixel lines of an image recording apparatus having a plurality of pixel lines extending in the main scanning direction and arranged in parallel in the sub-scanning direction and recording an image by performing an exposure in such a manner that the plurality of pixel lines are simultaneously recorded.
2. Description of the Related Art
Hitherto, there has been an image recording apparatus for recording, by its exposure head, an image on a recording material by rotating the recording material with wound around a recording drum thereof. An exposure head for use in the image recording apparatus of the type described above is arranged in such a manner that light emitting bodies such as LEDs are disposed on a stem. Optical beams emitted from the light emitting bodies are converged through a lens so as to be applied to the recording material. In an apparatus in which two light emitting bodies are disposed in the sub-scanning direction at a predetermined pitch, two pixels parallel to each other are exposed simultaneously in such a manner that two pixel lines are simultaneously recorded in parallel in the sub-scanning direction. Therefore, an advantage can be obtained in that the time taken to complete the recording of an image can be halved in comparison to a case in which the pixel lines are, one by one, recorded whenever the recording drum is rotated.
However, in the case where two pixels are simultaneously recorded at a predetermined pitch in the sub-scanning direction, the quality of image is deteriorated if the light emitting bodies in the sub-scanning direction are not disposed at a predetermined pitch, if the peak of the intensity of each of beams from the light emitting bodies deviates from the center line of the light emitting body and if the converging lens is distorted. The reason for the image quality deterioration lies in that since the pixels recorded on the recording material deviate from a predetermined pitch, the pixel lines recorded by scanning deviate from a predetermined pitch and the density of the recorded image is thereby periodically changed in the sub-scanning direction. That is, in the case where the interval between peak P.sub.1 of density A, in the sub-scanning direction, of the first pixel line recorded by a first light emitting body and peak P.sub.2 of density B, in the sub-scanning direction, of the second pixel line recorded by a second light emitting body becomes smaller than a predetermined pitch, as shown in FIG. 8, density D.sub.AB between the peak P.sub.1 of the density A and the peak P.sub.2 of the density B is raised and density D.sub.BA between the peak P.sub.2 of the density B and the peak P.sub.1 of the density A is lowered. Therefore, density C of the recorded image changes and deteriorates every two pixel lines in the sub-scanning direction.
In order to obtain a high quality image by eliminating the above-described periodical change of the density C of the recorded image, the accuracy in mounting the light emitting bodies must be raised, the peak of the intensity of each of the light emitting bodies must be made coincide with the center line of each of the light emitting bodies, and the distortion of the converging lens must be eliminated. However, the improvement of the mounting accuracy of the light emitting bodies arises a problem in that the manufacturing yield of the apparatus deteriorates. The measure taken to make the peak of the intensity of the optical beam from each of the light emitting bodies coincide with the center line of each of the light emitting bodies arises a problem in that the manufacturing cost of the light emitting body is raised. Furthermore, the measure to eliminate the distortion of the converging lens arises a problem in that the manufacturing cost of the converging lens is raised.
The present invention has been established for the purpose of overcoming the above-described problems. An object of the present invention is to provide an pixel interval compensating method for the purpose of obtaining a high quality image without the periodical density change in the sub-scanning direction without deteriorating the manufacturing yield of the apparatus and without raising the manufacturing cost of each of the light emitting body and the converging lens.